Sigma delta analog-to-digital converters (ADCs) are used in circuits to accurately convert a variety of test and measurement signals to digital values. Often, sigma delta ADCs are used in very low frequency applications that require high resolution. For example, a sigma delta ADC may be incorporated in a biopotential sensing circuit, i.e., a circuit configured to measure physiological signals, such as electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), pressure, tissue impedance, and motion signals.
Measuring intrinsic and evoked biopotentials requires amplifying authentic signals on the order of microvolts while rejecting large polarization potentials and environmental noise on the order of volts. In addition to these external disturbances, sigma delta ADCs fabricated with sub-micron processes have the additional burden of rejecting random telegraph signal (RTS) noise, also referred to as popcorn noise. RTS noise can produce random offsets that, some applications, may be large enough to be erroneously classified as sense events. Hence, RTS noise in an ADC can undermine the accuracy of a sensing device.